1. Field of the Invention
This invention relates to an electrically conductive material which is composed of titanium oxide crystal, and which can be used for making e.g. elements for optical or electrical devices, elements for gas detecting devices, or electrodes for electrochemical use, and a method of producing the same.
2. Description of the Related Art
If a light yellow and transparent crystal of titanium dioxide (TiO.sub.2) which is an electrical insulator is heated in a vacuum or in the presence of a reducing gas, such as H.sub.2 or CO gas, it is reduced to form an electrically conductive crystal having a blue or dark brown color. An electrically conductive material which is composed of such TiO.sub.2 crystals has already been used widely as a functional material in the electronic and chemical industries.
The conventionally available material has, however, a number of drawbacks which are due to the fact that when it is produced, the whole crystal of TiO.sub.2 is heated in a reducing atmosphere. The whole crystal is reduced and becomes electrically conductive. If a particular field of application calls for a crystal of TiO.sub.2 which is conductive only in a limited area, an additional work, such as cutting or grinding, is required. It not only makes it difficult to obtain a crystal having desired characteristics of conductivity, but also brings about a number of other problems including the breakage of the crystal and the adherence of foreign matter thereto.